1. Field of the Invention
The present invention concerns a process for producing aluminum oxide films by an ALD type process. According to the preferred process the aluminum oxide films are produced at low temperatures by bonding a metal compound on a substrate and converting said metal compound into a metal oxide.
2. Description of Related Art
Dielectric thin films with a high dielectric constant (permittivity) have a number of applications in the field of microelectronics. For example, they may replace the SiO2 and Si3N4 presently used in DRAM-memories in order to maintain the necessary capacitance as the size of capacitors is reduced.
Al2O3 films suitable for passivating surfaces have previously been prepared by physical processes, such as sputtering. The problem with the films produced by sputtering has been the unevenness of the resulting film, and the pinholes that are formed in the film. These pinholes may form a diffusion path for water through the film.
U.S. Pat. No. 6,124,158 discloses a method of reducing carbon contamination of Al2O3 thin films deposited by an ALD method. The ALD process uses organic aluminum precursors and water. In at least every third cycle, ozone is introduced into the reaction chamber to reduce carbon contaminants. The process has its limits since aluminum oxide films deposited below 190xc2x0 C. were not dense or reproducible.
ALD methods have also been used for producing Al2O3 films by using aluminum alkoxides, trimethyl aluminum (TMA) or AlCl3 as the aluminum source material and water, alcohols, H2O2 or N2O as the oxygen source material. Al2O3 films from TMA and water have been deposited at temperatures in the range of 150xc2x0 C. to 400xc2x0 C. Typically the temperature has been between 150xc2x0 C. and 300xc2x0 C. The resulting films had uniform thickness and did not contain any pinholes. However, the density of the film has been questionable at the lower end of the deposition temperature range.
In applications involving organic polymers or low molecular weight organic molecules, such as organic EL displays, the deposition temperature is preferably less than 150xc2x0 C., while in applications where the substrate is sensitive to water it is not feasible to use water as the oxygen source material. Thus there is a need for a process of producing aluminum oxide films by ALD at low temperatures using an oxygen source other than water.
The present invention is based on the surprising finding that high-quality aluminum oxide thin film can be grown by an ALD type process at substrate temperatures down to 100xc2x0 C. Another surprising finding is that ozone can be used in the deposition process without destroying the properties of substrates that contain an organic layer. A dense, pinhole-free thin film layer can be produced very quickly by ALD on the substrate surface, which protects the sensitive materials underneath the surface against the surrounding gas atmosphere.
In accordance with one aspect of the present invention a process is provided for depositing a thin film of aluminum oxide on a substrate by an atomic layer deposition process that comprises a plurality of cycles. Each cycle comprises supplying a first reactant that comprises a gaseous aluminum compound and supplying a gaseous second reactant that comprises a source of oxygen other than water. The second reactant converts the adsorbed portion of the first reactant on the substrate to aluminum oxide. Preferably the substrate is maintained at a temperature of less than 190xc2x0 C. during the ALD process.
A number of considerable advantages are obtained by means of the preferred embodiments. For example, with the aid of the present invention, it is possible to produce Al2O3 films of good quality at low temperatures.
Dielectric thin films with a dense structure can be used for passivating surfaces that do not tolerate high temperatures. Such surfaces include, for example, polymer films. If a water-free oxygen source is used, surfaces that are sensitive to water can also be passivated.
In addition, dielectric films, including aluminum oxide thin films, with a dense structure can be used as buffer layers between functional films that include at least one organic film. The dielectric film then prevents either reaction or diffusion between the functional films.